(1) Field of the Invention
The present invention relates to a vehicle speed control structure including a hydraulic clutch mounted on a propelling transmission line, a hydraulic actuator provided as part of a change speed apparatus, and a pilot operated switch valve mounted on an oil line extending to the hydraulic clutch. The switch valve is operatively connected to the hydraulic actuator for disengaging the hydraulic clutch upon start of a change speed operation by the actuator and engaging the clutch upon completion thereof. In particular, the invention relates to a hydraulic control system for controlling the hydraulic clutch and actuator.
(2) Description of the Prior Art
A known speed control structure as noted above is disclosed in Japanese Utility Model Publication No. 62-40351, for example. In this publication, a transmission case has a wall defining an opening which is closed by a lid. The lid carries a hydraulic actuator, a control valve for effecting change speed, and a pressure control mechanism for adjusting clutch pressure, all mounted on an inward face of the lid.
The lid is relatively large since these hydraulic devices are in a planar arrangement, and accordingly the opening defined in the wall of the transmission case is large. Thus, there is room for improvement in that the large opening tends to reduce the strength of the transmission case per se.
Further, the hydraulic actuator, control valve and the like mounted on the lid are interconnected by long piping. Since long piping presents considerable resistance to oil flows, delays tend to occur in the operation of the actuator. Improvement is desired in this sense also.